犬Marshall韧带心肌细胞短暂外向钾电流的特性

Characteristics of transient outward potassium current of canine cardiomyocytes in ligament of Marshall

目的 探讨Marshall束 (Marshallbundle ,MB)内心肌细胞短暂外向钾电流 (transientout wardpotassiumcurrent,Ito)的离子通道特性。方法 运用组织块酶解法分离犬MB内单个心肌细胞 ,在倒置显微镜下直接比较细胞形态 ;采用全细胞膜片钳技术记录MB内单个心肌细胞Ito电流密度及动力学特性。在细胞外液中加入 1μM异丙肾上腺素 ,比较加药前后Ito电流密度及动力学特性的变化。结果 MB内有两种形态迥异的心肌细胞 :一种为短矩形 ,短而宽 ,呈典型的矩形或略呈锥型 ;另一种为长杆型 ,长而窄。短矩形细胞数量明显多于长杆型细胞。短矩形细胞和长杆型细胞的长宽比分别为2 99± 0 95和 12 0 5± 2 4 1(P <0 0 1)。两种心肌细胞Ito的动力学无明显差别 ,但短矩形细胞的Ito电流密度明显小于长杆型细胞 ,8 77pA/pF (n =8)对 14 95 pA/pF (n =8) ,P <0 0 1。加用异丙肾上腺素后 ,在 +70mV ,长杆型细胞Ito峰值减小到 7 96pA/pF (n =8) ;短矩形细胞减小到 3 89pA/pF(n =8) ;两种细胞加药后Ito分别减小 (5 0 4± 0 32 ) pA/pF和 (6 86± 0 4 9) pA/pF (P <0 0 5 ) ;稳态激活曲线均右移 ,短矩形细胞与长杆型细胞的V1/ 2 分别从 (- 7 1± 0 8)mV和 (- 6 8± 0 7)mV变为 (-1 8± 0 2 )mV和 (- 1 6± 0 4 )

Objective The purpose of the study is to investigate the characteristic of transient outward potassium current(I to) of the myocytes in canine Marshall bundle.Methods The myocytes in ligament of Marshall were isolated using an enzyme dispersion technique.The length and width of myocytes were measured.The current density and dynamic properties of I to were studied by whole-cell patch-clamp techniques.Five minutes after isoproterenol added,the current density and dynamic properties of I to were measured again.Results There are two different shapes of cardiomyocytes in ligament of Marshall,one is rod shape,the other is short-rectangle shape.The short-rectangle myocyte is short and thick;the rod myocyte is long and thin.The number of short-rectangle myocyte is more than rod myocyte.The length/width ratio of short-rectangle myocyte is less than that of rod myocyte (2.99±0.95 vs 12.05±2.41,P<0.01).There were no difference of I to steady-state activation and inactivation properties between rod myocyte and short-rectangle myocyte,but current density of short-rectangle myocyte is significantly less than that of rod myocyte,8.77 pA/pF (n=8) vs 14.95 pA/pF (n=8),P<0.01.After isoproterenol added,the peak current density of I to of rod shape and short-rectangle shape decrease to 7.96 pA/pF (n=8) and 3.89 pA/pF (n=8) respectively,P<0.05;half-activation voltage (V 1/2) was shifted to positive,from (-7.1±0.8) mV and (-6.8±0.7) mV to (-1.8±0.2) mV and (-1.6±0.4)mV,the slope of curve did not alter;and steady-state inactivation curves of two kinds of cardiomyocytes was not changed.Conclusions There are two different myocytes in ligament of Marshall,the inhomogeneities of I to may be related to focal atrial fibrillation,isoproterenol can increase inhomogeneities of I to and trigger atrial fibrillation easier.